When I had my harliquins (they got killed by the damn hermits....) I just cut off a leg from the starfish and threw the rest in the freezer. I know, sound inhumane... but it works. This way your not having to remove bits of starfish that no one seems to want/wasting starfish. I managed to keep my 2 down to about a leg every few days to a week hence costs weren't too high. I have heard of harliquins doing alright on some of our local pacific starfish so you could always just go down to the docks at lowtide and find a starfish, chop its leg off and toss it back in. Try not to get any of the center and the starfish will regrow the leg and your harliquins will be happy (especially if the leg is pretty good size).
Something my dad told me about is when he left the NOAA ship that he hung out in Hood Canal with some of our extended family. They had a small scallop farm and would have infestations of starfish so to get rid of them they went out diving and took a knife to the starfish chopping them all up. Well little did they know that as long as the starfish have some of the center they can regenerate so a while after they had hundreds of "small" starfish infesting their farm.
So as I see it, it may be a little barbaric to chop off its leg and just throw it back, but they will certainly recover and come back in full force.